28 Days to Black Crumbly Humus from Nettles and Comfrey in a Rotol Compost Bin

Why Nettles and Comfrey Beat Most Green Waste

Stinging nettles (Urtica dioica) run roughly 2 to 3 percent nitrogen by dry weight, and comfrey (Symphytum) carries a heavy potassium load alongside decent nitrogen. That combination is what feeds a hot pile. The bacteria driving thermophilic decomposition need a carbon-to-nitrogen ratio somewhere near 25 or 30 to 1, and fresh green nettle cuttings sit well below that on their own. So they need bulking out.

The practical mix in a Rotol bin, which holds around 300 litres in the common size, is about two parts shredded nettle and comfrey to one part dry carbon. Straw, shredded cardboard, or last autumn’s collected leaves all serve. Chop the comfrey stems down to fist length or shorter. Whole stems stay wet and slimy in the middle of the pile for weeks, and you will find them intact at turning time, which stalls the whole batch.

One caution worth stating plainly: nettle seed heads and comfrey root fragments both survive cool composting. If the pile never reaches temperature, you are propagating both weeds straight back into the beds. The heat is the sterilising step, not an optional bonus.

The Hot Composting Method, Day by Day

Build the whole pile in one go. This is the single rule that separates a 28-day batch from a six-month one. A hot heap needs critical mass on day one, at least a cubic metre or a full Rotol bin packed to the brim, because a partially filled bin sheds heat too fast to sustain the microbial bloom.

Day 1: layer greens and browns, water each layer to the dampness of a wrung-out cloth, and seal the lid. By day 2 or 3 the core should be too hot to hold a hand in. A cheap compost thermometer with a 30 cm probe, the kind sold for under fifteen pounds, tells you what is actually happening. You want 55 to 65 degrees Celsius. Above 70 and the beneficial organisms start dying off and the pile goes anaerobic and sour.

Turn on day 4, again on day 8, then every four to five days after. Each turn moves the cooler outer material into the hot centre and reintroduces oxygen. The temperature will spike again within a day of each turn, then taper. By roughly day 24 to 28 it stops reheating after a turn, the material has gone dark and crumbly, and the nettle smell has been replaced by something closer to woodland floor. That flat temperature response is your finish signal, more reliable than any calendar date.

Moisture is the variable people get wrong. Too dry and the bacteria stall; too wet and you squeeze out the air. If squeezing a handful produces more than a drop or two of liquid, add dry cardboard at the next turn.

Sieving the Leaf Mould You Set Aside

Leaf mould works on a different clock entirely. It is fungal, cold, and slow, taking twelve to eighteen months in a wire cage or a bin liner punched with holes. Do not expect it inside a month.

When it is ready, run it through a 10 mm garden riddle. The fines that fall through make an excellent seed-sowing medium on their own or blended half and half with sharp sand. What stays on top, the leaf ribs and twiggy bits, goes back into the next hot batch as carbon.

Feeding the Lawn Around the Composting Cycle

Seaweed feed and finished humus do different jobs on turf, and the timing matters more than the products. Liquid seaweed, whether Maxicrop or a supermarket own-brand extract, is a biostimulant heavy in trace elements and cytokinins, not a heavy nitrogen feed. Diluted to the bottle rate and watered on in spring and again in early autumn, it greens up the sward and supports root recovery, but it will not push the lush top growth a straight nitrogen feed produces.

A Wolf-Garten spreader, or any calibrated drop spreader, is the tool that stops you scorching stripes into the grass. The mistake is walking faster over one patch than another and doubling the rate at the turns. Set the spreader to the granule’s stated setting, do the lawn in one direction, then a second pass at right angles at half the rate. That cross-hatch evens out the inevitable overlaps.

Sieved compost from your finished Rotol batch makes a spring top-dressing. Spread it 3 to 5 mm thick and work it into the sward with the back of a rake or a stiff broom until it disappears between the grass blades. Any thicker and you smother the leaf. This feeds soil biology in a way granular fertiliser never touches, and over two or three seasons it visibly improves how the lawn holds up in a dry August.

A rough worked example: a 100 square metre lawn top-dressed at 4 mm depth needs about 400 litres of sieved compost, which is more than one full Rotol batch yields. So most gardeners dress in sections across successive years, prioritising the thin and worn patches near paths and gates.

Bokashi as the Front End for Kitchen Scraps

Cooked food, meat scraps, and citrus peel all cause trouble in an open compost bin, drawing rats and turning slimy. A bokashi bucket ferments them first. The bran-borne Lactobacillus and yeast cultures pickle the waste anaerobically over about two weeks in a sealed bin, dropping the pH low enough to stop putrefaction.

The fermented output is not finished compost. It is a pre-digested, sharply acidic mass that needs burying in a trench or folding into the centre of a hot Rotol pile, where the low pH neutralises fast and the material breaks down within days. Drain the leachate from the tap every couple of days; diluted 1 part in 100 with water it goes on as a soil drench, though it is far too strong neat.

Iron Sulphate and the Moss Problem

Moss in a lawn is a symptom, usually of shade, compaction, poor drainage, or scalping the mower too low. Iron sulphate at roughly 5 grams per square metre, watered in or applied as ferrous sulphate in a spring lawn sand, blackens moss within days and lets you rake it out. It also deepens the green of the grass through the iron itself.

But killing the moss does nothing about why it arrived. If the ground stays compacted, the moss returns by the following autumn. Hollow tine aeration is the mechanical fix: a hollow-tine fork or a powered aerator pulls out cores of soil 8 to 10 cm deep, leaving open channels that let air and water into the root zone. On heavy clay this makes more difference to moss than any amount of iron sulphate.

There is a sequencing question here that catches people out. Do you scarify first to rake out the dead moss and thatch, then aerate, then top-dress the holes with sieved compost and sharp sand? Or aerate first so the scarifier does not just tear at a compacted surface? On a badly matted lawn the order changes the result, and it is worth deciding before you hire the machine for the weekend.